Stagnant pollution mixture Possible
Daily PM2.5 peaked at 86.9 µg/m³ near Riverside across 1 covered metro home to 4.7 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 15 million cigarettes. An awareness illustration of outdoor exposure at 22 µg/m³ per cigarette (Berkeley Earth), counting only the event's ranked days; not a medical dose.
Why we think this happened
The October 7 Rubidoux peak sits inside a four-day western Inland Empire PM2.5 buildup that appears regional on both surrounding network sampling days. NWS documented an approximately 1,900-foot inversion, stratus moving into the Inland Empire, then exact-date dense fog, a thinning marine layer, and weak onshore flow. Established South Coast source characterization supplies the recurring secondary-plus-combustion mixture. This supports stagnant anthropogenic mixture at possible confidence, while the rotating monitor schedule and missing exact-day speciation prohibit a stronger or source-specific claim.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA AirData hypothesis
EPA's certified daily record measured 86.9 micrograms per cubic meter at Rubidoux on October 7. It was the only 24-hour FRM PM2.5 monitor in the metro reporting that date, so the exact-day number cannot by itself establish metro-wide spatial coverage.
National Weather Service San Diego Area Forecast Discussion via Iowa Environmental Mesonet · Oct 6, 2003 hypothesis
NWS measured an inversion base near 1,900 feet on October 6 while low clouds moved into the Inland Empire. The exact-date October 7 discussion then reported dense fog, a thinning marine layer, and weak onshore flow. These observations document persistent shallow-layer retention during the rising PM2.5 sequence.
Inference, not direct attribution
rotating_monitor_episode_plus_shallow_inversion_and_basin_profile_possible.v1: This inference is recorded in the catalog methodology.
Evidence path
A cause is more convincing when the record connects three things: something happened, the air mass moved toward the region, and local instruments responded. Here is how much of that chain is documented for this event.
Source or mechanism
rotating_monitor_episode_plus_shallow_inversion_and_basin_profile_possible.v1. This inference is recorded in the catalog methodology.
Air-mass movement
The retained record does not yet show how air traveled from the proposed source to these metros. A trajectory replay or dated plume analysis belongs here.
Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 4.0 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓Event autopsy
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Riverside-San Bernardino-Ontario, CA
Monitor comparison window 2003-10-04 to 2003-10-10 · PM2.5 target: Rubidoux
62% above nearby days
1 calm hour observed
Haze reported during 1 hour
62% higher than surrounding days
About the same as surrounding days
11% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
12 kt maximum · 1 of 24 observed hours calm
0 observed hours at or below 3 miles
72°F to 95°F
52% maximum
Source: U.S. EPA AirData daily observations and, where available, nearby ASOS/AWOS surface observations. Values are descriptive medians over the retained monitor set; missing measurements remain missing. Transport and source evidence remain separate layers because this instrument pattern does not assign a cause by itself.
Episode peak
-- cigarettes
The smoke map's scale, replayed over this event: the surface interpolates between covered metros' daily records, framed to the affected region. Hover for a reading, click a metro to pin it to the card. Days a monitor did not report draw nothing.
Views from the selected metro
Select a metro on the map to see nearby cameras. Where an operator archive reaches the event, drag the divider to compare two moments, adjust either date and time, or play the available event-day frames. Camera imagery is visual context, not an air-quality measurement or proof of smoke.
No useful public camera views are currently available within 80 km of this metro.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Riverside-San Bernardino-Ontario, CA | 86.9 µg/m³ | 4.0 | Oct 7, 2003 | #17 of its top days |
"Cigarettes, whole event" totals a metro's ranked event days at 22 µg/m³ per cigarette: what a person outdoors there breathed across the event, as the illustration. "All-time standing" is where this episode's days sit in each metro's ranked record (worst-area measure, since 1999). Full local context is on each metro's Air Records page.
Public evidence library
Each card states what a source supports—and what it does not. Official records, research, reporting, community observations, and transparent inferences remain visibly different kinds of evidence.
National Weather Service San Diego via Iowa Environmental Mesonet
NWS San Diego expired a dense-fog advisory on the event morning and reported a thinning marine layer and weak onshore flow; it did not identify a PM2.5 cause.
Context for the event; this item does not establish the attributed cause by itself.
Dense fog and a marine layer are context only; this discussion does not explicitly document a trapping inversion or emitting source.
National Weather Service San Diego Area Forecast Discussion via Iowa Environmental Mesonet
NWS measured an inversion base near 1,900 feet on October 6 while low clouds moved into the Inland Empire. The exact-date October 7 discussion then reported dense fog, a thinning marine layer, and weak onshore flow. These observations document persistent shallow-layer retention during the rising PM2.5 sequence.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The sounding was taken at San Diego and does not measure the Rubidoux mixing height directly.
U.S. EPA AirData
The surrounding certified samples show that October 7 sat inside a coherent western Inland Empire episode rather than standing alone. On October 6, Rubidoux, San Bernardino, and Ontario measured 77.4, 73.9, and 66.9 micrograms per cubic meter. On October 9, Rubidoux, Riverside-Magnolia, Ontario, Fontana, and San Bernardino measured 76.6, 73.3, 68.9, 64.3, and 62.5, while desert and mountain sites remained 17 or lower. Rubidoux itself stayed above 76 from October 6 through 9.
Context for the event; this item does not establish the attributed cause by itself.
These adjacent-day network samples reconstruct the episode around a rotating FRM schedule; they are not measurements from every site on October 7.
U.S. EPA AirData
EPA's certified daily record measured 86.9 micrograms per cubic meter at Rubidoux on October 7. It was the only 24-hour FRM PM2.5 monitor in the metro reporting that date, so the exact-day number cannot by itself establish metro-wide spatial coverage.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One reporting monitor cannot establish the exact-day regional footprint.
Kim et al., Journal of the Air & Waste Management Association
A South Coast AQMD-led characterization found that ammonium, nitrate, sulfate, organic carbon, and elemental carbon dominated basin PM2.5, with especially high inland concentrations at Rubidoux. It establishes the recurring secondary-plus-combustion mixture available to accumulate under the observed shallow-layer conditions.
Context for the event; this item does not establish the attributed cause by itself.
The study is recurring basin context, not an October 7, 2003 chemical sample.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
This episode was grouped from the monitor record by the catalog pipeline and given its cause from the evidence listed above. It has not been individually reviewed and signed off, so its boundaries, cause, and name may change as evidence accumulates. Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the assembled evidence above, not an IAQng detection formula. If it is wrong, tell us.